20/20
-the
expression for normal eyesight (or 6/6 in countries where metric measurements
are used). This notation is expressed as a fraction. The numerator (1st number)
refers to the distance you were from the test chart, which is usually 20 feet (6
meters). The denominator (2nd number) denotes the
distance at which a person with normal eyesight could read the line with the
smallest letters that you could correctly read. For
example, if your visual acuity is 20/100 that means that the line you correctly
read at 20 feet could be read by a person with normal vision at 100 feet. The Snellen chart, which consists of letters, numbers, or symbols, is used to test
visual acuity (sharpness of eyesight). A refraction test is used to determine
the amount of correction needed for a prescription when treating refractive
error such as astigmatism, myopia, or hyperopia. See 'Refraction Test'.

Ablation Removal.
In vision, ablation refers to the surgical removal of eye tissue to
correct a refractive error such as myopia.

AC/A Ratio-
accommodative convergence / accommodative (measured in prism
diopters/diopters). The convergence response of an individual (amount the eyes
turn inward) in relation to the amount of stimulus of accommodation (eye
focusing). The normal ratio is 4:1.

Accommodation-(eye focusing) the eye's
ability to adjust its focus by the action of the ciliary muscle, which increases
the lens focusing power. When this accommodation skill is working properly, the
eye can focus and refocus quickly and effortlessly, which is similar to an
automatic focus feature on a camera. The ciliary muscles must contract to adjust
for near vision, which causes the eye's crystalline lens, which is flexible, to
be squashed. For distant vision, the ciliary muscle must relax and the eye's
crystalline lens is stretched out. The ability of the eye to accommodate
does decrease with age due to the crystalline lens becoming less flexible
causing a condition called presbyopia. (See "Presbyopia").
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Accommodative Esotropia-
(clinical condition) when an individual is focusing on a near object and his or
her eyes are turning inward too much. It is caused by either uncorrected
hyperopic refractive error and/or a high accommodative convergence/accommodation
(AC/A) ratio. The average age of onset is 2 1/2 years. It is most noticeable
when the child is tired or sick. This
is treated with plus lenses (glasses or contacts) to help straighten the
eyes. In some cases, vision therapy and corrective lenses are prescribed.
(Please note that Accommodative Esophoria is a condition similar to
accommodative esotropia but lesser in extent.)
Accommodative Excess (AE)-
This clinical condition is also called accommodative spasm. It is an over
focusing, over stimulation of the focusing action of the crystalline lens
causing an inability to relax the focusing system which may result in blurry
vision when focusing at distance objects. Other symptoms include holding near
work closer than normal, headaches with near work (such as reading or using a
computer), eyestrain associated with near work, and possible double vision.
Clinical signs include: patient accepts more minus on accommodative rock but
blurs with plus lenses, lower NRA than PRA, dynamic retinoscopy findings
indication of over accommodation and/or slow relaxation of accommodation, and
reduced or erratic distance visual acuity. Treatment includes a low plus lens
and/or vision therapy.

Accommodative Fatigue-
This clinical condition is also called Ill-Sustained Accommodation. It is
the inability of the eye to adequately sustain sufficient focusing over an
extended time period. The most common sign or symptom is blurred vision after
prolonged near work such as reading and using a computer. In addition, such
patients often have asthenopia (eyestrain), general fatigue, headaches and
nausea, excess tearing, and an unusual sensitivity to light. Clinical signs
include: normal amplitude of accommodation, decreased PRA, and the patient
generally fails the +/-2.00 D flipper test. Plus lenses (glasses or contacts)
and vision therapy are effective in treating this condition.

Accommodative Infacility-
a clinical condition in which the individual has difficulty changing eye focus
from distance to near. Symptoms include eyestrain associated with near work
(such as reading or using a computer), periodic blurring of distance vision
especially following sustained near visual work, tendency to hold near work
closer than expected, headaches with near work, and possible double vision.
Clinical signs include: patient will have difficulty with both the plus and the
minus lens (fails +/- 2.00 D flipper test), low PRA and NRA, and poor recoveries
on Bell Retinoscopy. Vision therapy is an effective treatment option.

Accommodative
Insufficiency (AI)-
This clinical condition is also called non-presbyopic accommodative
insufficiency. It is an under focusing, a lack of focusing ability at a near
distance. Symptoms include eyestrain, blurred vision, occasional or constant
when doing near work (such as reading or using a computer), occasional unusual
sensitivity to light, excess tearing, headaches, and general fatigue. Clinical
signs include: patient will have difficulty with a minus lens, low amplitude of
accommodation, low PRA and higher NRA. Vision therapy is an effective treatment
option.
Accommodative Vergence-
a convergence
response (to turn the eyes inward) which occurs as a direct result of
accommodation (eye focusing). (See "Vergence")

Acetate-
Type of plastic often used in eyeglass frames.

Acuity-
clearness of eyesight. Depends on the sharpness of images and the sensitivity of
nerve elements in the retina. (See "Near Acuity" and "Distance Acuity")

Add-prescription strength of a
plus lens which is used for near vision. A plus lens can be added to another
lens such as a minus lens for distance vision. (See "Bifocal Glasses" and
"Presbyopia")

After-image- the eye's ability to still see an
image during eye blinks and even after the viewed object is no longer present.
The most common example is seeing light after the flash of a camera.

AK- (astigmatic keratotomy) Procedure in which a surgeon cuts the cornea
so that is more spherical when it heals, thus reducing astigmatism.

Albinism
- pigmentation is deficient or absent. May occur in skin, hair, and eyes. Ocular
albinism is a pigmentation deficiency occurring mainly in the eyes. Individuals
with albinism including ocular albinism commonly have decreased visual acuity
(20/70 -20/200), strabismus, photophobia, and nystagmus. There is no known
treatment. Individuals may benefit from low-vision aids. Treatment options for
strabismus and nystagmus does apply to these individuals. For more information
about albinism,
click here. (See
'Strabismus' and 'Nystagmus')

Alignment-
proper fusing (uniting) of images to each eye.

Amblyopia-
(clinical
condition) reduced visual acuity (poorer than 20/20) which is not correctable by
glasses or contacts and is not caused by structural or pathological anomalies.
This condition is often called 'lazy eye' because it is typically the result of
disuse. It is usually marked by blurred vision in one eye and favoring one eye
over the other. About two percent of the population is affected.

Types of functional (reversible) amblyopia:

refractive- anisometropia (the
two eyes have different refractive powers), or other
amblyopiogenic refractive errors (hyperopia, myopia, or astigmatism)

strabismic- misalignment of the two eyes in which they point in different
directions

form deprivation (may also be referred to as amblyopia ex anopsia)-
caused by conditions that prevent light from entering the eye. These may
include congenital ptosis (droopy eyelid), corneal opacity, or cataract.

Ametropia- any
optical error such as hyperopia, myopia, or astigmatism. Also called refractive
error.

AMD or ARMD-
(age-related macular degeneration) Disorder characterized by the gradual loss of
central vision due to a damaged macula (which is made up of retinal cones
necessary for sight).

Amplitude of Accommodation (AA)-
a measurement of the eye's ability to focus clearly on objects at near
distances. This eye focusing range for a child is usually about 2-3 inches. For
a young adult, it is 4-6 inches. The focus range for a 45-year-old adult is
about 20 inches. For an 80-year-old adult, it is 60 inches.

Angle- (angle
In glaucoma), "angle" refers to the drainage channel for the aqueous humor in
the eye; improper drainage can lead to the high intraocular pressure associated
with glaucoma. In narrow-angle glaucoma, the channel is blocked, whereas
open-angle glaucoma has other causes, such as the body producing too much
aqueous humor.

Aniseikonia-
a difference
in the size or shape of two visual imageswhen the images
should be the same size and/or shape.

Anisometropia- the condition in which the two eyes
have different refractive powers.

Anomalous Retinal Correspondence (ARC)- a type of retinal projection,
occurring frequently in strabismus, in which the foveae (center of the retina
that produces the sharpest eyesight) of the two eyes do not facilitate a common
visual direction; the fovea of one eye has the same functional direction with an
extrafoveal (non-fovea) area of the other eye.

ANSI Z87.1-
The American National Standards Institute's Practice for Occupational and
Educational Eye and Face Protection; eyewear that meets this standard is
considered safer than eyewear that does not.

Anterior Chamber-
Part of the eye behind the cornea and in front of the iris and lens.

Antioxidant-
Substance that inhibits oxidation and can guard the body from the damaging
effects of free radicals. Molecules with one or more unpaired electrons, free
radicals can destroy cells and play a role in many diseases. Antioxidants may
help prevent macular degeneration and other serious eye diseases.

Antireflective coating-
(AR coating) Thin layer(s) applied to a lens to reduce the amount of reflected
light and glare that reaches the eye.

Aqueous Humor-
Clear fluid in the eye that both provides nutrients and determines intraocular
pressure.

Aspheric-
Not quite spherical. Aspheric eyeglass lenses are popular among people who have
strong prescriptions because they are thin and lightweight, and reduce
distortion and eye magnification. Aspheric contact lenses can work as a
multifocal, or to correct a single-vision problem like astigmatism.

Associate of the College
of Optometrists in Vision Development-individual who is licensed optometrist for at least two years and
provides developmental and behavioral vision care services including vision
therapy. Associate members must obtain at least 10 hours of continuing education
annually in functional / developmental/ behavioral / rehabilitation vision care.
The optometrist has not sat for his/her certification exams, therefore is not
Board
Certified in Vision Development and Therapy.

Asthenopia-
eyestrain, symptoms include excessive tearing, itching, burning, visual fatigue,
and headache. It can be caused from an uncorrected refractive error,
accommodation (eye focusing) disorder, binocularity (eye teaming) disorder, or
by extended, intense use of the eyes.

Astigmatism-
light rays entering the eye do not all meet at the same point (similar to a
frayed string), which results in blurred or distorted vision. An abnormally
shaped cornea typically causes this condition. Occasionally
astigmatism exists in the lens of the eye.
This condition is corrected by a cylindrical (toric) eyeglass or contact lens.

Automated Refractor-
also called auto refractor. This method determines the eye's refractive error and the best
corrective lenses to be prescribed by using a computerized device that varies
its optical power mechanically and prints out the results.

Axis-
the alignment
of the len's cylindrical part; used for correcting astigmatism. This measurement
is given in degrees. The values are typically from 90 degrees to 180 degrees.

Band Keratopathy-Opacity of the eye's stroma
and Bowman's membrane.

Base-Down (BD) Prism- a wedge-shaped lens which is thicker on one edge
than the other. The thicker edge (base) is turned down. Prisms bend light
(opposite direction from its thicker end) so the base-down prism turns the light
upward thus causing the eye to also move up. This prism is used to measure an
eye misalignment and/or treat a binocular dysfunction (eye teaming problem).
Prisms are sometimes added to glasses to help improve eyesight due to a
misalignment or visual field loss.

Base-In (BI) Prism-
a wedge-shaped lens which is thicker on one edge than the other. The thicker
edge (base) is turned inward, closest to the nose. Prisms bend light (opposite
direction from its thicker end) so the base-in prism turns the light outward
(toward the ear) thus causing the eye to also move outward. This prism is used
to measure an eye misalignment and/or treat a binocular dysfunction (eye teaming
problem). Prisms are sometimes added to glasses to help improve eyesight due to
a misalignment or visual field loss.

Base-Out (BO) Prism-
a wedge-shaped lens which is thicker on one edge than the other. The thicker
edge (base) is turned outward, closest to the ear. Prisms bend light (opposite
direction from its thicker end) so the base-out prism turns the light inward
(toward the nose) thus causing the eye to also move inward. This prism is used
to measure an eye misalignment and/or treat a binocular dysfunction (eye teaming
problem). Prisms are sometimes added to glasses to help improve eyesight due to
a misalignment or visual field loss.
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Base-Up (BU) Prism-
a wedge-shaped lens which is thicker on one edge than the other. The thicker
edge (base) is turned up. Prisms bend light (opposite direction from its thicker
end (base)) so the base-up prism turns the light downward thus causing the eye
to also move down. This prism is used to measure an eye misalignment and/or
treat a binocular dysfunction (eye teaming problem). Prisms are sometimes added
to glasses to help improve eyesight due to a misalignment or visual field loss.
Behavioral Optometrist-
also called Functional Optometrist or Developmental Optometrist.
An optometrist who specializes in all aspects of vision as it is related to an
individual's development and to the role of vision in relation to reading, computer monitor use, and
sports. The optometrist may use prescription lenses and/or vision
therapy to improve an individual's visual function and performance.
Behavioral optometry had its origins in orthoptics, which is a non-surgical
treatment for strabismus, and in case analysis systems which were developed to
resolve eyestrain symptoms that
include excessive tearing, itching, burning, visual fatigue, and headache
in nonstrabismic individuals. Behavioral optometry's emphasize of visual care is
in prevention, remediation, rehabilitation, and enhancement.
(See "Fellow
of the College of Optometrists in Vision Development (FCOVD)")

Bifocal Glasses-
used to correct vision at two distances, composed of two ophthalmic lenses such
as a plus lens for near vision and a minus lens for distance vision.

Bi-lateral Integration/
Gross Motor Coordination-
visual guidance of body movements and the coordination between both sides of the
body.

Binocular Fusion Dysfunction-
a clinical
condition in which the eyes are not working as a team. Vision
therapy is an effective treatment option. (See"General Binocular Vision Disorder")

Binocular Vision-
the simultaneous use of the two eyes.

Binocularity-
the ability to use both eyes as a team and to be able to fuse (unite) two visual
images into one,
three-dimensional image (See 'Convergence' and 'Divergence').

Botulinum Toxin Type A (Oculinum, BotoxTM)- an injection of this poison
has been used as an alternative to conventional surgery in selected strabismic
patients. It causes a temporary paralysis of an extraocular muscle that leads to
a change in eye position. This change has been reported to result in
long-lasting and permanent alteration in eye alignment. Although one injection
is often sufficient to produce positive results, one-third to one-half of
patients may require additional injections. This technique has been most
successful when used in adults with small-angle misalignments. It is not
commonly used in children. This treatment is also used in patients who have
blepharospam (an uncontrollable eye lid spasm).

Bowman's Membrane- Corneal layer between the epithelium and the stroma.

Break Point- the
point at which a person can no longer fuse (unite) two images into one. A blur
point will occur before the this point.

Brewster Stereoscope-
an instrument used in orthoptics/vision therapy to improve eye teaming skills
and near focusing skills. It consists of two parallel viewing tubes with a +5.00
D lens. The distance from the target can be adjusted as well as the pupillary
distance. The Bernell-O-Scope and Keystone Ophthalmic Telebinocular are designed
essentially the same.

Bridge-
The part of eyeglasses that extends across the nose.

Cable temple- Style of eyeglasses that wraps around the ear,
to keep them well-fastened.
Cataract- a
condition of the crystalline lens, in which the normally clear lens becomes
clouded or yellowed, causing blurred or foggy vision. Cataracts may be caused by
aging, eye injuries, disease, heredity, or birth defects. Surgery is a treatment
option. The affected lens is removed and is replaced with a substitute (implant)
lens or with a special type of contact lens. Generally the success rate of
cataract surgery is over 90%, if the eye is otherwise healthy.

Central island- Refractive surgery complication in which the laser leaves
an "island" of corneal tissue in the concave ablation zone. Symptoms include
double vision and distortion.

Cheiroscope- an
instrument used in orthoptics/vision therapy to train binocular skills and
accommodation skills. The Keystone Correct-Eye Scope is an example of a
Cheiroscope.

Choroid- Layer of blood vessels and pigments (usually brown or blue) that
lies beneath the sclera (the white of the eye). Often mistakenly called the
iris.

Ciliary Body -
a structure
directly behind the iris of the eye and contains the ciliary muscle.

Ciliary Muscle-
a band of muscle and fibers that are attached to the lens that controls the
shape of the lens and allows the lens to accommodate (change focus).
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CMV retinitis- (cytomegalovirus retinitis) Serious eye infection usually
found in those with immune problems, such as AIDS patients; symptoms include
floaters, blind spots, blurry vision and vision loss.

Collagen-
Fibrous protein in bones and connective tissue, it is also present in the eye.
One type of vision correction surgery heats collagen around the edges of the
cornea (which lets light into the eye). This procedure reshapes the cornea,
helping it focus light right onto the retina, for clearer vision.

Color Perception Test-
a test that measures the ability to identify and distinguish colors.Color Vision
Deficiency-
also known as Colorblindness. It is the absence of or defect in the
perception of colors. Color vision is based on perception of red, green, and
blue. If there is a defect in the perception of one of these colors, a color
will be perceived as if it were composed only of the other two colors. Based on
the color or colors for which there is defective perception, a person may suffer
from red, green, or blue blindness. Color blindness in which all colors are
perceived as gray is termed monochromasia. For people with the common,
inherited, types of color deficiency there is no cure.

Comitant Strabismus-
a condition in which the magnitude of deviation remains essentially the same in
all positions of gaze and with either eye fixating.
Computer Vision Syndrome (CVS)-
the complex of eye and vision problems related to near work that are experienced
during or related to computer use. Its symptoms include eyestrain, dry or
burning eyes, blurred vision, headaches, double vision, distorted color vision,
and neck and backaches. The condition is caused by various internal and external
factors. Treatment options may include prescription glasses and/or vision
therapy.

Conductive Keratoplasty-
(CK) Procedure wherein a surgeon uses radio waves to heat collagen in the
cornea's periphery to shrink it and reduce hyperopia.

Cone - a
receptor cell which is sensitive to light and is located in the retina of the
eye. It is responsible for color vision.

Conjunctiva- Mucous membrane that lines the visible part of the eye and
the inner surface of the eyelid.

Conjunctivitis-
an inflammation of the conjunctiva, the transparent layer covering the inner
eyelid and the white portion (sclera) of the eyeball. Conjunctivitis can be
caused by a virus, bacteria, or fungus (infectious conjunctivitis, or "pink
eye", may be contagious); by allergies to pollen, fabrics, animals, or cosmetics
(allergic conjunctivitis); or by air pollution or noxious fumes such as swimming
pool chorine (chemical conjunctivitis). Symptoms include red or watery eyes,
blurred vision, inflamed inner eyelids, scratchiness in the eyes, or (with
infectious conjunctivitis) a puss like or watery discharge and matted eyelids.
Conjunctivitis is usually treated with antibiotic eye drops and/or ointment.

Convergence-
the ability to use both eyes as a team and to be able to turn the eyes inward to
maintain single vision up close.

Convergence Excess (CE)-
a clinical condition in which the eyes have a tendency to turn excessively
inward when viewing an object at a near distance. Symptoms may include visual
fatigue while reading or using a computer, occasional blurred or double vision,
and inability to comprehend or concentrate while reading. Clinical signs
include: greater esophoria at near than distance, high AC/A ratio, and a high
lag of accommodation. Can be improved with vision therapy and/or glasses. (See
"Esophoria")

Convergence Insufficiency (CI)-
(clinical condition) the inability of the eyes to turn inward and/or sustain an
inward turn. Symptoms include eye strain with reading and using a computer,
headaches, loss of comprehension, difficulty concentrating, blurred or double
vision, and eye fatigue. Clinical signs include: near point of convergence of
greater than 4 inches (10 cm), greater exophoria at near than at distance, and
low AC/A ratio. Vision therapy is an effective treatment option.

Cornea-
the transparent, blood-free tissue covering the central front of the eye (over
the pupil, iris, and aqueous humor) that initially refracts or bends light rays
as light enters the eye. Contact lenses are fitted over the cornea.

Corneal Abrasion-
Tearing or puncture of the cornea. Usually causes pain, tearing, light
sensitivity, and a feeling that something is in the eye.

Corneal Implants-
Devices (such as rings or contacts) placed in the eye, usually to correct
vision.

Corneal Ring-
Type of vision correction surgery where a doctor inserts a tiny plastic ring
into the cornea (which lets light into the eye). This ring reshapes the cornea,
helping it to focus light better onto the retina so you can see better. The ring
can be adjusted and even removed if desired.

Corneal Topography-
Process of using a camera/computer system to map the cornea for refractive
surgery, contact lens fitting and corneal disease management.

Corneal Ulcer-
Wound in the surface of the eye caused by injury, dryness due to lack of tear
production, or infection.

Cover Test- a
test of eyeball alignment in which each eye is covered with an occluder (eye
cover) and then uncovered to observe eye movements.

COVTT-
Certified Optometric Vision Therapy Technician. To be certified an
individual must be employed by a Fellow (FCOVD), provide documentation of 2000
hours or 2 years of direct clinical experience in vision therapy; or 1000 hours
of clinical experience if the individual holds an AA degree or higher with
emphasis in the behavioral sciences. Submit written answers to a series of Open
Book Questions dealing with various aspects of vision function, testing and
therapy. Pass an extensive written and oral examination evaluating the
candidate's knowledge and clinical abilities in behavioral vision, vision
development and vision therapy. COVTTs must obtain at least 6 hours of
continuing education annually in functional / developmental / behavioral vision
care.

Cystoid Macular Edema- (CME) Swelling of the eye's macula, caused by an
excessive amount of fluid.

Crystalline Lens-
transparent disc located behind the iris which changes shape to focus on objects
at different distances from the eye.

Cycloplegic Refraction-
one method available to eye doctors to determine the eye's refractive error and
the best corrective lenses to be prescribed if needed. The eye is dilated with
the muscles of accommodation (eye focusing muscles) being temporarily paralyzed
with specialized eye drops or spray (Atropine, Homatropine, Cyclogyl, or
Mydriacyl). This is a good method for non-responsive or non-communicative
patients such as young children. The technique of retinoscopy is used with this
method. (See 'Retinoscopy')

Cylinder Lens- an
ophthalmic lens that has at least one non-spherical surface. Used to correct
astigmatism. The values are typically from -0.75 to -1.25. The cylinder
measurement is given with a "-" sign. (Please note that the sign for myopia
(nearsightedness) is also "-".)

Dacryostenosis- Blocked tear duct, which is
characterized by a lot of tearing.

Diabetic Retinopathy- Leaking of retinal blood vessels in advanced or
long-term diabetes, affecting the macula or retina. Vision can be seriously
distorted or blurred.

Diopter (D)- a
measurement of the refractive (light bending) power of a lens or a prism
(pd). The strength of prescription glasses and contacts are measured in these
units. For example a lens that is 0.50 diopter (D) is very weak, where as a lens
that is 10.0 diopter (D) is very strong.
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Diplopia- a single
object is perceived as two rather than one; double vision.

Direct Occlusion-
covering the non-amblyopic eye. (See "Inverse Occlusion" and "Occlusion")
Directionality/Laterality-
directionality relates to the awareness of the relationship of one object in
space to another / laterality relates to the internal awareness of the two sides
of the body. Directionality/Laterality can also be called spatial relations.

Directionality/LateralityDisorder- a condition in which an individual has poor development of
left/right awareness. Symptoms of this disorder include confusion of right and
left direction and letters and/or numbers reversals. Vision therapy is a helpful
treatment option.
Distance Acuity-
the eye's ability to distinguish an object's shape and details at a far distance
such as 20 feet (6 meters).

Divergence- the
ability to use both eyes as a team and be able to turn the eyes out toward a far
object.

Dominant Eye- the
eye that "leads" it partner during eye movements. Humans also have dominant
hand, foot, eye, and side of the brain (not necessarily all on the same side).

Drusen- Small yellow or white deposit in the eye. Drusen are sometimes
signs of macular degeneration.

Dry Eye- Lack of sufficient lubrication and moisture in the eye. Most dry
eye complaints are temporary and easily relieved; dry eye syndrome is chronic
and needs more advanced treatment by an eyecare practitioner.

Duction Test- a
test of the eye's ability to turn inward or outward while maintaining single,
binocular vision with the gradual introduction of progressively stronger base-in
or base-out prisms.

Dysphoneidesia-
inability to "sound out" words and poor sight recognition of words.
Dysphoneidesia is a subtype of dyslexia. Its characteristics are a combination
of the other two forms of dyslexia: Dysphonesia and Dyseidetic.

Dysphonesia-
inability to "sound out" words. Dysphonesia is a subtype of dyslexia. Children
with this form of dyslexia have difficulty sequentially analyzing and
remembering what and where the sounds are in words. The resulting phonemic
processing problems make it difficult to sound out new words, learn phonics, and
make them dependent on their sight vocabulary. When they come to an unknown word
they will often substitute a word using context clues. For example, "pony" for
"horse", even though the substituted word doesn't look or sound anything like
the original word. When spelling unknown words it is often difficult to
determine what the original word is. For example, they may write "fmlue" for
"familiar" or "lap" for "lamp". They cannot learn phonics because they cannot
process where the sounds are. Their short term sequential auditory memory can be
poor and result in repeating "8167" as "8671", or remember to go to their room
but forgetting to get the item requested.
Dyseidetic- poor sight recognition of words. Dyseidetic is a subtype of
dyslexia. Children with this form of dyslexia have trouble analyzing and
remembering written symbols. They continue to confuse the orientation. For
example, they will write numbers and letters backwards long after other children
have mastered these skills. They often confuse letter sequences in reading, and
in spelling often get all the letters but in the wrong sequence (spelling "dose"
for "does", "on " for "no", etc.). Their visual memory for words is poor,
and after learning a new word they may fail to recognize that same new word
later in the sentence. They have trouble learning to read and spell phonetically
irregular words. For example, they may read " laugh" as "log" and spell it as
"laff", both of which are phonetically consistent. Their spelling will have many
mistakes, but will be phonetically consistent and one can usually tell what the
word was they were trying to spell. When they are attempting to read an unknown
word they will usually attempt to sound it out and do so very slowly.
Dyslexia - a
specific language-based disorder.
The
individual has difficulty with letter or word recognition, spelling, reading,
writing, and sometimes naming pictures of objects.
Dyslexia
varies in degree from mild to very severe.
It is caused by an inability of the brain's language centers to decode print or
phonetically make the connection between the word's written symbols and their
appropriate sounds. Dyslexia is not caused by a vision disorder. Children often
are of normal or above normal intelligence. Dyslexia cannot be cured and will
never be outgrown. Appropriate teaching methods can be taught to help those with
dyslexia overcome their weakness. The
Dyslexia Determination test which is used by many optometrists who specialize in
vision related vision problems investigates if the patient has one of the three
forms of dyslexia: Dyseidetic - poor sight recognition of words,
Dysphonesia- inability to "sound out" words, and Dysphoneidesia - a combination
of characteristics from both types. Vision therapy is NOT considered a direct
treatment for dyslexia.

Eccentric Fixation-
the deviating eye does not use the central foveal (center of the retina that
produces the sharpest eyesight) area for fixation. Commonly, individuals with
amblyopia and some individuals with strabismus will have this visual adaptation.
In esotropia, the eccentrically located retinal point used for fixation is
usually in the nasal retina. In exotropia, the eccentrically located retinal
point used for fixation is usually in the temporal retina.Vision therapy is a treatment
option for those with amblyopia and/or strabismus. It is not a treatment option
for an individual with a fovea that has been destroyed.

Emmetropia-
normal vision, no correction needed.

Esophoria (Eso)-
(clinical condition) a tendency of the eyes to want to turn more inward than
necessary when an individual is viewing an object at near or at distance, which
may cause the individual to experience eyestrain and other symptoms. Symptoms of
basic esophoria include: eyestrain, headaches, blurred or double vision,
apparent movement of print, and difficulty concentrating on and comprehending
reading material. Clinical signs of basic esophoria include: AC/A ratio is
normal, equal esophoria at distance and near, and normal near point of
convergence. Sometimes esophoria is caused by a refractive error such as
hyperopia (farsightedness), and glasses or contacts can correct the problem
alone. However, sometimes vision therapy is needed to to help re-train the eyes
to function more appropriately.

Endothelium- The cornea's inner layer of cells.
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Epithelium- The cornea's outer layer of cells.
Esotropia (ET)-
(clinical condition) a condition in which an eye is turned either constantly or
intermittently inward toward the nose. Esotropia is a type of strabismus. It is
caused by a reduction in visual acuity, reduced visual function, high refractive
error, traumatic brain injury, oculomotor nerve lesion, or eye muscle injury.
Treatment options may include one or more of the following: glasses or contacts,
bi-focal lenses, prisms, vision therapy, surgery, or Botulinum Toxin Type A
(Oculinum, BotoxTM) injections. In some cases, esotropia is caused by
a refractive error such as hyperopia (farsightedness), and glasses or contacts
alone may allow the eyes to straighten. Vision therapy is most appropriate when
there are small degrees of misalignment. Surgery, to re-position or shorten the
eye muscles, may be required for high degrees of misalignment. If surgery is
required, a combination of surgery and vision therapy often yields the best
results.

Exophoria (Exo)-
(clinical condition) a tendency of the eyes to want to turn more outward than
necessary when an individual is viewing an object at near or at distance, which
may cause the individual to experience eyestrain and other symptoms. Symptoms of
basic exophoria include: eyestrain, headaches, blurred or double vision,
apparent movement of print, and difficulty concentrating on and comprehending
reading material. Clinical signs of basic exophoria include: normal AC/A ratio,
equal exophoria at distance and near, and decreased near point of convergence.
Vision therapy is an effective treatment option.

Exotropia (XT)-
(clinical condition) a condition in which an eye is either constantly or
intermittently turned outward toward the ear. Exotropia is a type of strabismus.
It may also be called divergent strabismus, wandering eye, or wall eye(s). It is
caused by a reduction in visual acuity, reduced visual function, high refractive
error, traumatic brain injury, oculomotor nerve lesion, or eye muscle injury.
Treatment options may include one or more of the following: glasses or contacts,
bi-focal lenses, prisms, vision therapy, surgery, or Botulinum Toxin Type A
(Oculinum, BotoxTM) injections. Vision therapy is most appropriate
when there are small degrees of misalignment. If surgery is required, a
combination of surgery and vision therapy often yields the best results. For
more information, please
click here. To see the American Optometric
Association's guidelines for vision therapy, please
click here.
(See 'Strabismus')

Extraocular Muscles-
the muscles attached to the outside of the eyeball which control eye movement.
Each eye has six muscles (lateral rectus, medial rectus, superior oblique,
inferior oblique, superior rectus, and inferior rectus) that are coordinated by
the brain.

Facility of Accommodation- a measure of the ease and
speed of the eye(s) to change focus.

Farsighted- Also called hyperopia. To farsighted people, near objects are
blurry, but far objects are in focus.

Fellow of the College of Optometrists in Vision Development (FCOVD)-
individual who is a licensed optometrist for a minimum of three years and
directly involved in vision therapy for a minimum of 2 years, has completed a
guided study program, submitted evidence of 100 hours of continuing education in
functional vision (and vision therapy), and passed rigorous written, oral,
and clinical examinations. Fellows are Board Certified in Vision Development and
Therapy and must obtain at least 15 hours of continuing education annually in
functional / developmental / behavioral / rehabilitation vision care.

Figure-Ground-
the ability to recognize distinct shapes from their background, such as objects
in a picture, or letters on a chalkboard.

Fixation- the
ability to direct and maintain steady visual attention on a target. Fixations
are a form of pursuits.
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Fixation Disparity (FD)-
over-convergence or under-convergence, or vertical misalignment of the eyes
under binocular (both eyes) viewing conditions small enough in magnitude so that
fusion is present.Flap and Zap- Slang for LASIK.

Floaters-
also known as spots, are usually clouded or semi-opaque specks or
particles within the eye that are seen in the field of vision.The eyes
are filled with fluid which maintains the shape of the eye, supplies it with
nutrition and aids in the focusing of light. Often, particles of protein or
other natural materials are left floating or suspended in this fluid when the
eye is formed before birth. If the particles are large or close together, they
cast shadows which make them visible. This is particularly true when
nearsightedness occurs or becomes more severe. In most cases this is normal but
floaters can also be caused by certain injuries, eye disease or deterioration of
eye fluid or its surrounding structures.

Form Constancy-
the ability to recognize two objects that have the same shape but different size
or position. This ability is needed to tell the difference between "b" and "d",
"p" and "q", "m" and "w".

Fovea-
center of the retina that can produce the sharpest eyesight and contains the
most cones. (See
diagram
of the eye)

Fusional Vergence- a convergence response which
serves to maintain (fusion) the union of images from each eye into a single
image. The eyes will turn with a slow smooth tonic movement or a fast jumping
movement called phasic.

Fusion- the union
of images from each eye into a single image. There are three degrees of
fusion. 1st
degree fusion is the superimposition of two dissimilar targets. 2nd
degree fusion is flat fusion with a two-dimensional target. 3rd
degree fusion is depth perception (stereopsis) with a three-dimensional target.

Fusion Test-
determines the eyes ability to unite the images from each eye into a single
image.

General Binocular Vision Disorder- inability to efficiently utilize and/or sustain
binocular vision. Symptoms include eyestrain, headaches, decreased
comprehension, inability to concentrate while reading, excessive tearing, and
blurred vision. A patient will have difficulty with both base-in and base-out
prisms. Vision therapy is an effective treatment option.

Glaucoma- Disease characterized by excessive fluid (aqueous humor) in the
eye, high intraocular pressure and vision impairment. Blindness can result.

Heterophoria-
tendency of the eyes to deviate from their normal position for visual alignment.
This condition may be observed when one eye is covered.

Heterotropia-
the eyes are abnormally turned.

Higher-Order Aberration- Irregularity of the eye other than a refractive
error (myopia, hyperopia or astigmatism). Higher-order aberrations sometimes
affect your vision (such as decreasing contrast sensitivity), and sometimes do
not.
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High Index- Type of lens with a higher index of refraction, meaning that
light travels faster through the lens to reach the eye than with traditional
glass or plastic. It is denser, so the same amount of visual correction occurs
with less material (whether glass or plastic), so the lens can be thinner.

HTS Computerized Binocular Home Vision Therapy System
- a computer program which is prescribed by an eye doctor. The computer program
is for improving eye tracking, eye teaming, and/or eye focusing.
Hyperopia-
farsightedness, an individual will have difficulty seeing clearly up close.
Light entering the eye focuses behind the retina when the eye is at rest and is
corrected with a plus lens. Vision therapy is not prescribed for hyperopia.
Children, up to about the age of 8 years, are often farsighted.

Hyperphoria- a
condition in which one eye has a tendency to point higher than the other eye,
causing eyestrain. Sometimes improved by prisms in glasses.
Hypertropia-
strabismus,one eye turned in anupward
direction.
Hypophoria- a
condition in which one eye has a tendency to point lower than the other eye.
This condition may be observed when one eye is covered.

Hypotropia-
strabismus, one eye turned in adownward direction.

Hysterical Amblyopia- anon specific
visual loss with an unknown cause. Upon examination the doctor is unable to find
corroborating objective evidence of this abnormality. The most common symptom is
an isolated visual acuity impairment, followed by combined visual acuity
impairment and visual field constriction, and whereas an isolated visual field
constriction occurred most infrequently. Thisvision loss may be due to
anxiety or emotional repression.(See "Streff Syndrome")

Ill-Sustained Accommodation-
this clinical condition is also called Accommodative Fatigue. It is the
inability of the eye to adequately sustain sufficient focusing over an extended
time period. The most common sign or symptom is blurred vision after prolonged
near work such as reading and using a computer. In addition, such patients often
have asthenopia (eyestrain). Clinical signs include: normal amplitude of
accommodation, decreased PRA, and the patient generally fails the +/-2.00 D
flipper test. Plus lenses (glasses or contacts) and vision therapy are effective
in treating this condition.

IncomitantStrabismus - a condition also known as
Noncomitant Strabismus. It occurs when the magnitude of deviation is not the
same in the different positions of gaze or with either eye fixating. There
is an abnormal restriction to movement or an over-action of one or more of the
extraocular muscles. Generally, the magnitude must change by at least 5 PD to be
incomitant (nonconcomitant).

Intraocular Lens- (IOL) Artificial lens that a cataract surgeon places in
a patient's eye after removing the eye's natural lens. Like a contact lens, it
has a built-in refractive power tailored specifically to the patient's visual
condition.

Intraocular Pressure- (IOP) Eye pressure, as determined by the amount of
aqueous humor filling it. High IOP (ocular hypertension) can be a sign of
glaucoma.
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Iris-
the colored part of the eye located between the lens and cornea; it regulates
the entrance of light.

Iritis- Inflammation of the iris.

Keratectomy- Surgical removal of part of the cornea.

Keratitis- Inflammation of the cornea.

Keratoconus- Condition in which the cornea develops a cone-shaped bulge that
can result in major blurring and distortion.

Keratoplasty- Any of several types of corneal surgery, such as shrinking the
collagen to reduce farsightedness or transplanting a new cornea to treat
keratoconus.

keratotomy- Incision of the cornea.

Kinesthesia-
the sensation of bodily position, presence, or movement resulting chiefly from
stimulation of sensory nerve ending in muscles, tendons, and joints.Lacrimal Plug- Device to block the lacrimal punctum (an
opening at the end of a tear duct), to keep the eye moist.

Lag of Accommodation- a measure of the eye's ability to focus accurately on
a given target. The dioptric difference between the eye's focusing response and
the stimulus to focus.

Laser Photocoagulation- Procedure in which a surgeon uses a laser to
coagulate tissue, usually to seal leaking blood vessels and destroy new ones in
diseases like macular degeneration and diabetic retinopathy.

LASEK- (Laser Epithelial Keratomileusis) Procedure that is similar to
LASIK, except that the surgeon cuts a flap in the epithelium only, instead of
through the epithelium and part of the stroma. LASEK is used mostly for people
with thin or flat corneas who are poor candidates for LASIK, which requires more
corneal tissue for success.

Laser Thermal Keratoplasty- (LTK) Also called Laser Thermokeratoplasty.
Surgery to correct mild farsightedness in people over 40; the doctor uses a
holmium laser to heat the cornea and shrink its collagen.
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LASIK- (Laser-Assisted In Situ Keratomileusis) Surgical procedure in
which a tiny flap is cut in the top of the cornea, underlying corneal tissue is
removed with an excimer laser, and the flap is put back in place. LASIK corrects
myopia and hyperopia.

Lateral Rectus- muscle Muscle that moves the eye away from the nose.
Latent Hyperopia-
hyperopia (farsightedness) is compensated by accommodation and the tonicity
(tension) of the ciliary muscle; identified by cycloplegic refraction. In mild
cases of hyperopia (farsightedness), the eyes are able to compensate without
corrective lenses; otherwise a plus lens (glasses or contacts) is
prescribed. Vision therapy is not prescribed. (See "Hyperopia")

Learning Disability (LD)- a
disorder that affects people's ability to either interpret what they see and
hear or to link information from different parts of the brain. Learning
disabilities can be divided into five broad categories: speech and language
disorders, reading disorder, arithmetic disorder, writing disorder, and
attention disorders. The term learning disability does not include children who
have learning problems that are primarily the result of visual, hearing, or
motor disorders.

Lensometer- also
called Verometer, is a device used to measure the refractive power of
eyeglasses and contact lenses.

Limbus- Boundary area connecting the cornea and sclera; the three form
the eye's outermost layer.

Lipid- A fatlike substance that can collect on contact lenses, making
them uncomfortable.

Low Vision- Also called partial sight. Sight that cannot be
satisfactorily corrected with glasses, contacts, or surgery. Low vision usually
results from an eye disease such as glaucoma or macular degeneration.

Lutein- An antioxidant that is found throughout the body, but is
concentrated in the macula. Lutein is believed to help protect the eyes from
free radical damage caused by the sun's harmful rays.

Macula-
the most sensitive part of the retina that is about the size of a pinhead and is
where our most detailed vision occurs.

Maculopathy- Disease of the macula, such as age-related macular
degeneration.
Macular Degeneration -
a
deterioration of the central portion of the retina known
as the macula.
Click here for
information.

Malingering- a
voluntary or intentional reduction in visual acuity or other examination data.

Medial Rectus- muscle Muscle that moves the eye toward the nose.

Microcornea- Abnormally small cornea.

Microkeratome- Small instrument that surgeons use to cut the cornea.
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Microstrabimus
- also called microtropia, monofixation syndrome, and small
angle strabismus. A small angle deviation (inward or outward, commonly
inward) that is less than five degrees with some amount of stereopsis (depth
perception) and anomalous retinal correspondence(ARC). Possible mild
amblyopia, eccentric fixation, and/or anisometropia may also be present. It
frequently results from the treatment of a larger-angle deviation (esotropia or
exotropia) by optical correction, vision therapy, pharmacological agents, and/or
extraocular muscle surgery. Treatment for microstrabimus consists mostly of
correcting significant refractive errors and any coexisting amblyopia. The use
of vision therapy and prisms to establish bifoveal fusion has been successful in
selected cases.

Migraine- (ocular) Visual phenomena that may accompany a migraine
headache or that may occur without any headache. They include light flashes,
spots, wavy lines, flickers, zig-zagging lights, semi-circular or
crescent-shaped visual defects and distortions of shapes.

Minus (-) Lens-
concave lens, stimulates focusing and diverges light. The lens is thinner in the
center than the edges. It is used in glasses or contact lenses for people who
are nearsighted (myopia).
Monocular Vision-
only one eye having useful vision.

Myasthenia Gravis- Autoimmune disease sometimes related to thyroid
conditions. Signs are droopy eyelids or double vision that worsen toward the end
of the day.

Myopia-
nearsightedness, an individual will have difficulty seeing clearly at distance.
Light entering the eye focuses in front of the retina when the eye is at rest
and is corrected with a minus lens. A condition known as high myopia occurs when
myopia is greater than 6 diopters. Typically, vision therapy is not prescribed
for myopia.

Near Acuity-
the eye's ability to distinguish an object's shape and details at a near
distance such as 16 inches (40 cm).

Nearsighted- Also called myopia. Condition in which visual images come to
a focus in front of the retina, resulting in defective vision of distant
objects.

Near Point of Convergence (NPC)- the closest point at which the two eyes
can maintain a single united image.

Near Point of Convergence Test-
measures the patient's ability to point the eyes at an approaching object and to
keep them fixed on the object as it reaches the patient's nose. Normal
range is 0 to 4 inches away from the nose.

Negative Relative Accommodation (NRA)-
a measure of the maximum ability to relax accommodation while maintaining clear,
single binocular vision.

Neovascularization- Abnormal growth of new blood vessels, such as in an
excessive amount, or in tissue that normally does not contain them.

Nevus- Also spelled naevus. Brown pigmentation resembling freckle or mole
on white of the eye. More often found in dark-skinned people. Sometimes
malignant.
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Nickel- Metallic element used mainly in alloys. Many eyeglass frames are
made of nickel alloy, so people who are allergic should choose a hypoallergenic
substitute, such as titanium.

Normal Retinal Correspondence (NRC)- the foveas of the two eyes are corresponding neural points in the
visual cortex and binocular vision can occur.

Nystagmus- rhythmic
oscillations or tremors of the eyes which occur independent of the normal eye
movements. Generally nystagmus is not curable, but it is manageable. Treatments
include prescription glasses or contact lenses, prisms, and vision therapy.

Occlusion-
to block out light. An eye can be completely or partially blocked. This
procedure is used to promote the use of one eye or both eyes. This therapy
procedure may be used for people with amblyopia, strabismus, or closed head
trauma. It may also be used in a vision therapy program for someone with
amblyopia, eye focusing (accommodation) disorder, or poor eye tracking
(oculomotor) skill. An eye patch, black contact, or another device may be
used to block out light from an eye. (See "Direct Occlusion" and "Inverse
Occlusion")

Ocular Hypertension- Condition in which the intraocular pressure of the
eye is elevated above normal and which may lead to glaucoma.
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Oculomotor Skills-
the ability to quickly and accurately move our eyes. These are sensory motor
skills that allow us to move our eyes so we can fixate on objects (fixation),
move our eyes smoothly from point to point as in reading (saccades), and to
track a moving object (pursuits). (See "Fixation", 'Pursuits' and 'Saccades')
Oculus Dexter (OD)- right eye.

Oculus Sinister (OS)- left eye.

Oculus Uterque (OU)- both eyes.

Ophthalmologist -
a physician (doctor of medicine (M.D.) or doctor of osteopathy (D.O.) who
specializes in the comprehensive care of the eyes and visual system in the
prevention of eye disease and injury. The ophthalmologist has completed four or
more years of college premedical education, four or more years of medical
school, one year of internship, and three or more years of specialized medical
and surgical training and experience in eye care. The ophthalmologist is a
physician who is qualified by lengthy medical education, training and experience
to diagnose, treat and manage all eye and visual system problems, and is
licensed by a state regulatory board to practice medicine and surgery. The
ophthalmologist is the medically trained specialist who can deliver total eye
care: primary, secondary and tertiary care services (i.e., vision services,
contact lenses, eye examinations, medical eye care and surgical eye care), and
diagnose general diseases of the body. An ophthalmologist is not trained to
provide vision therapy.

Ophthalmoscope- a
device used to illuminate the inside of the eye and enlarge the image for
examining the retina, optic nerve entrance, arteries, and veins.

Optic Nerve-
is a bundle of nerve fiber that connects each eye to the brain and transmits
images from the retina to the brain.

Optic Nerve Head- Also called optic disk. Circular area where the optic
nerve enters the retina, and the location of the eye's blind spot.

Optician- is a
professional in the field of designing, finishing, fitting and dispensing of
eyeglasses and contact lenses, based on an eye doctor's prescription. The
optician may also dispense colored and specialty lenses for particular needs as
well as low-vision aids and artificial eyes.

Optometric Vision Therapy (VT)-
as defined by the American Optometric Association: Optometric vision therapy is
a treatment plan used to correct or improve specific dysfunctions of the vision
system. It includes, but is not limited to, the treatment of strabismus (turned
eye), other dysfunctions of binocularity (eye teaming), amblyopia (lazy eye),
accommodation (eye focusing), ocular motor function (general eye movement
ability), and visual-perception-motor abilities. Optometric vision therapy is
based upon a medically necessary plan of treatment which is designed to improve
specific vision dysfunctions determined by standardized diagnostic criteria.
Treatment plans encompass lenses, prisms, occlusion (eye patching), and other
appropriate materials, modalities, and equipment. (Vision therapy can also be
called visual or vision training, orthoptics, eye training, or eye exercises.)

Optometrist - a
health care professional who is state licensed to provide primary eye care
service. These services include comprehensive eye health and vision
examinations; diagnosis and treatment of eye disease and vision disorders; the
detection of general health problems; the prescribing of glasses, contact
lenses, low vision rehabilitation, vision therapy, and medications; the
performing of certain surgical procedures; and the counseling of patients
regarding their surgical alternatives and vision needs as related to their
occupations, avocations and lifestyle. The optometrist has completed
pre-professional undergraduate education in a college or university and four
years of professional education at a college of optometry, leading to the doctor
of optometry (O.D.) degree. Some optometrists complete a residency.

tobacco-alcohol amblyopia- clinical evidence exists that a nutritional
deficiency is the underlying cause of this vision loss; however, many still
believe that the toxic effects of alcohol and/or tobacco are contributing
factors.

Orthokeratology- (ortho-k) Procedure in which a doctor fits you with special
gas permeable contact lenses to reshape your cornea and correct errors like
nearsightedness. Often, patients wear the lenses just at night.

Orthophoria (ortho)-
the absence of either esophoria or exophoria. The eyes do not have a tendency to
want to turn more inward than necessary or want to turn more outward than
necessary when pointed on an object.

Orthoptics-
the science of correcting defects in binocular vision. The technique of eye
exercises to correct strabismus (esotropia or exotropia), convergence
insufficiency (exophoria), or convergence excess (esophoria), amblyopia, and
ocular motility disorders. Orthoptics was pioneered by French ophthalmologist
Javal in the mid to late 1800's. Today ophthalmologists use specialty-trained
healthcare professionals called orthoptists to evaluate patients and treat them
with orthoptics. In America, the non-surgical technique of orthoptics is less
commonly used by ophthalmologists compared to other countries. Orthoptics is a
limited form of optometric vision therapy.

overconvergence-
Condition in which the eyes come too far inward when focusing on a near object,
resulting in blurring.

Papilla- Small bump where the optic nerve exits the eye.

Paresis- a paralysis that when occurring in ocular muscles causes double
vision when looking in some directions.

Pars Plana- Posterior part of the eye's ciliary body.

Penalization- to
prevent sight out of the good eye and force the weaker, amblyopic eye, to
function. A filter, eye patch, or eye drops such as atropin or miotics are used
on the good eye.

Perceptual Skills-
includes the identification, discrimination, spatial awareness, and
visual-sensory integration. These are visual cognitive skills used to processes
visual information to the brain to be organized and interpreted. (See 'Visual
Perceptual Disorder')

Perimetry- the
measurement of a visual field function (the total area that can be seen while
looking straight ahead) using targets of different sizes and brightness (light
levels). The visual field is measured in degrees. In a normal eye the peripheral
field of vision is about 180 degrees. An instrument called a perimeter is used
for mapping all areas of a person's eyesight, including peripheral (side)
vision. Visual field testing can help detect certain patterns of visual loss,
indicating specific types of eye diseases or vision conditions. It is the single
best test for diagnosing glaucoma.

Peripheral Vision-
the ability to see or be aware of what is surrounding us, our side vision. (See
"Visual Field".)

Phasic- fast, jump
movement. (See "Fusional Vergence")

Photoablation- Procedure in which a surgeon uses ultraviolet radiation to
remove tissue.

Photochromic- Able to change lens color or darkness/density depending
upon the degree of exposure to light.

Photokeratitis- "Sunburn" of the cornea; symptoms include discomfort,
blurred vision, and light sensitivity. The temporary vision loss that can result
is called "snow blindness."

Photophobia-
unusual sensitivity to light.

Photorefractive Keratectomy-
(PRK) Surgical procedure in which an excimer laser is used to remove corneal
tissue to correct vision problems.

Pingueculum- Yellowish, thickened lesion on the conjunctiva. May be
caused by irritation from sun, dust and wind.

Physiological Diplopia- a normal diplopia (double
vision) that occurs when an individual is not pointing his/her eyes on a certain
object.

Plano Lens- a lens
that has no prescription. No variance between the curvature of the front and
back lens surfaces. It is a flat lens.

Pleoptics- a
method of eye exercises created to stimulate and train an amblyopic eye. The
goal is to have eyesight which is produced by the fovea. (See "Eccentric
Fixation")

Plus (+) Lens-
convex lens (thicker in the middle) relaxes focusing and converges light. It is
typically used in glasses or contact lenses for people who are farsighted
(hyperopic). Although it may also be prescribed for other visual conditions as
well.

Polaroid Lens- a
lens used in sunglasses and sometimes 3D glasses which consists of two glass or
plastic surfaces with a plastic lamination between the two surfaces, and
designed to reduce reflected glare. In optometric vision therapy, these lens are
used with 3D pictures such as vectograms and stereograms, which are also
polarized.

Polycarbonate- Lens material that is very impact-resistant, thinner than
plastic, and is used for spectacle lenses.

Polymethyl Methacrylate-
(PMMA) Old-fashioned hard contacts were made of PMMA, which is not permeable;
today's rigid lenses contain other polymers that allow oxygen to reach your eye.

Positive Relative Accommodation (PRA)- a measure of the maximum
ability to stimulate accommodation while maintaining clear, single binocular
vision.

Posterior Chamber- Part of the eye behind the iris and in front of the
lens.

Presbyopia-
sometimes called the fourth refractive error, is not truly a refractive error.
It is the natural process of the eye losing the ability to accommodate or change
the shape of the natural crystalline lens inside the eye to see comfortably at
near. This vision defect occurs with the advancement of age; the onset usually
occurs between the ages of 40 to 45. Unlike the rest of the body, which stops
growing by the age of twenty, the lens of the eye continues to grow throughout
life. As the lens ages and grows, it becomes harder in consistency, loses its
elasticity, and therefore is resistant to changes in shape. The result is a
gradual reduction in accommodation (near eye focus), and a more dependence on
reading glasses. A plus lens or multi-focal lens (such as a bifocal lens) is
prescribed in the form of glasses or contact lenses. For more information,
please
click here. Vision therapy is not a treatment option.

Prism-
a wedge-shaped lens which is thicker on one edge
than the other. This plastic or glass lens bends light (opposite direction from
its thicker end). Prisms can be used to measure an eye misalignment and/or treat
a binocular dysfunction (eye teaming problem). A prism is sometimes added to
glasses to help improve eyesight due to an eye misalignment or
visual field loss.
(See "Base-Down Prism", 'Base-In Prism', 'Base-Out Prism',
"Base-Up Prism", "Yoked Prism")

Prismatic Effect By Lens-
when light goes through a wedge shaped lens which is called a prism, it bends.
Light is also bent when it does not go through the center of a lens. This is an
undesirable effect that can occur in glasses. It commonly occurs when the
pupillary distance (PD) is not measured or made correctly.

Progressive Lenses- (also, progressive addition lenses or PALs)
Multifocal lenses whose corrective powers change progressively throughout the
lens. A wearer looks through one portion of the lens for distance vision,
another for intermediate vision, and a third portion for reading or close work.
Each area is blended invisibly into the next, without the lines that traditional
bifocals or trifocals have.

Propionate- A soft, flexible material that is sometimes used in goggles.

Proximal Vergence- a convergence response
attributed to the awareness of, or the impression of nearness of an object of
regard. (See "Vergence")

Pseudomyopia-
the condition Accommodative Excess/Spasm causes an individual to experience
blurry distance vision after prolonged near work such as reading or using a
computer. The individual may appear to be nearsighted (myopia). Treatment
options may include prescription lenses and/or vision therapy.

Pterygium- Triangular-shaped fold of tissue on white of the eye. May
eventually grow over part of the cornea. May be caused by irritation from sun,
dust and wind.

PTS Computerized Perceptual Home Vision Therapy System-
a home-based computerized perceptual therapy program, which was designed to
enhance visual information processing. The therapy procedures address
simultaneous processing, sequential processing and/or speed of information
processing. This computer program contains 6 activities that are specifically
for the following problems: a weakness with visual information processing skills
such as figure-ground, form constancy, spatial relations, visual closure, visual
discrimination, visual memory, and visualization skills, slow speed of
information processing, and acquired brain injury with perceptual-cognitive
deficits. This program is available only from a licensed eye care practitioner.
Pupil-
the opening at the center of the iris of the eye. It contracts (dilates) in the
dark and when the eye is focused on a distant object.

Pupillary Distance (PD)-
the distances between the pupils of the eyes, in millimeters.

Pupillary Reflex-
the automatic contraction or enlargement of the pupil when confronted with the
presence or absence of light, accommodation, or emotional change.

Pupillometer- a
device used to measure the distance between the pupils of the eyes, in
millimeters. It
also measures the diameter of the pupil.

Pursuit Dysfunction-
a condition in which the individual's ability to follow a moving target is
inadequate. Vision therapy is an effective treatment option.

Pursuit Test-
measures the eyes ability to follow a moving target.

Pursuits- the
eye's ability to smoothly follow a moving target.

Radial Keratotomy-
(RK) Surgical procedure where cuts are made in the cornea in a radial pattern,
to flatten the cornea and correct myopia.
Reading- requires the use of good visual skills, which are distance and near
acuity, accommodation skills, binocularity
skills (convergence), oculomotor skills (saccadic), peripheral
vision, figure-ground, form constancy, spatial relations, visual closure, visual
discrimination, visual memory, and visualization.

Refraction Test-
determines the eye's refractive error and the best corrective lenses to be
prescribed. There are several methods of performing refraction: Retinoscopy,Automated Refractor, and Subjective Refraction.

Refractive Error-
defects in vision caused by the eye's inability to bend, or refract light and
focus it clearly on the retina. Astigmatism, hyperopia, and myopia are common
conditions of refractive error, also called ametropia.

Refractive Power-
a lens' ability to bend parallel light rays into focus, as measured by power
diopters. In general, the greater the curvature of a lens and the greater the
difference between center thickness and edge thickness, the higher the index of
refraction and the greater its refractive power. Refractive power can also refer
the strength of a person's contact lenses or glasses.
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Refractive Media-
the parts of the eye that light travels through before being focused on the
retina includes the cornea, crystalline lens, aqueous, and vitreous. (See
diagram of the eye)

Refractive Surgery- Surgery that corrects visual acuity, with the
objective of reducing or eliminating the need for glasses and contacts. Includes
radial keratotomy, PRK, LASIK, and corneal implants.

Relative Amblyopia-
functional amblyopia can co-exit with a pathology abnormality. Treatment is
possible.

Retina-
the innermost layer of the eye, a neurological tissue, which receives light rays
focused on it by the lens. This tissue contains receptor cells (rods and cones)
that send electrical impulses to the brain via the optic nerve when the light
rays are present. (See
diagram of the eye)

Retinal Detachment- Condition where the retina separates from the
choroid.

Retinitis Pigmentosa- Condition characterized by the progressive loss of
peripheral vision, usually beginning with night blindness.

Retinoscopy-
this technique determines the eye's refractive error and the best corrective
lenses to be prescribed. An instrument called a retinoscope which consists of a
light, lens, mirror, and handle, is used to shine light into a patient's eye.
There are two types of retinoscope: streak and spot retinoscope. When light is
shone into patient's eye, the light is reflected back ('reflex'). If the
reflection is in the same direction ('with movement') of the retinoscope then
the refractive error is hyperopia (farsightedness) and a plus lens is
prescribed. If the reflection is in the opposite direction ('against movement')
of the retinoscope then the refractive error is
myopia (nearsightedness) and a minus lens is prescribed. The strength of the
prescription is determined when the pupil is suddenly filled with light
('neutralized') with the appropriate lens powers (strength). There are other
types of retinoscopy such as Static retinoscopy or Dynamic retinoscopy.

Rigid Gas Permeable-
(RGP) Type of contact lens made of breathable plastic that is custom-fit to the
shape of the cornea. RGPs are the successor to old-fashioned hard lenses, which
are now virtually obsolete.

Rod-
a
receptor cell which is sensitive to light and is located in the retina of the
eye. It is responsible for night vision (non-color vision in low level light).

Saccades-
the eye's ability to direct and coordinate movement as it quickly and
voluntarily shift from one target to another.

Saccades Dysfunction-
a condition in which the individual's ability to scan along a printed page and
move his eyes from point to point is inadequate. Symptoms include frequent loss
of place while reading, skip or transpose words, and have difficulty
comprehending because of an inaccurate eye movement. Vision therapy is an
effective treatment option.

Saccadic Test-
measures the eyes ability to move quickly and precisely from point to point.

Sclera-
the white protective covering of the eye.

Slit Lamp (Biomicroscope) - this
instrument can
examine ocular tissue from the front of the cornea
to the back of the lens. A narrow "slit"
beam of very bright light produced by a lamp. This beam is focused on to the eye
which is then viewed under magnification with amicroscope. A joystick
control is employed to enable instrument to be moved left-right and up-down. A
chin rest, head rest and fixation target is also required. Some slit lamps have
a tilting mechanism to enable the lamp to be directed from different angles.
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Spatial Relation-
the ability to judge the relative position of one object to another and the
internal awareness of the two sides of the body. These skills allow the
individual to develop the concepts of right, left, front, back, up, and down.
This ability is needed in reading and math. (See "Directionality/Laterality")

Sphere- an
ophthalmic lens with no cylindrical power or addition. It has the same power in
all parts of the lens.

Squint- to be
unable to direct both eyes simultaneously toward a point. Also known as
strabismus (turned eye).
For more information, see
"Strabismus".

Stereopsis- the
ability to perceive a three dimensional depth which requires adequate fusion
(union) of the images from each eye.

Stereopsis Test-
measures depth perception that is dependent on the accuracy of eye teaming.

Strabismus-
(clinical condition) turned eye (s), the eyes are misaligned. It is caused by a
reduction in visual acuity, reduced visual function, high refractive error,
traumatic brain injury, oculomotor nerve lesion, or eye muscle injury. In
strabismus, the eyes send conflicting images to the brain, and the brain cannot
combine these images as it would in normal vision. The brain compensates by
ignoring one image in favor of the other, causing a loss of depth perception.
Strabismus in more common in children, and affects four percent of all children
(although it may also appear later in life).

Strabismus is also known as squint. It may also be
referred to as cross-eyes (convergent- turning inward) or wall eyes (divergent-
turning outward). Treatment options may include one or more of the following:
optical lenses, bi-focal lenses, prisms, surgery, vision therapy, or Botulinum
Toxin Type A (Oculinum, BotoxTM) injections.

Streff Syndrome-
named after the optometrist who originally described it, Dr. John Streff. This
functional vision loss is also known as Non-Malingering Syndrome. Signs include
reduced visual acuity in both eyes at distance and near. The visual acuity at
near is more reduced than the distance acuity. Frequently patients will have
reduced stereopsis, large accommodative lag on dynamic retinoscopy, and a
reduced visual field (tubular or spiral field). The syndrome is associated with
a visual or emotional stress occurring in the child's life. It is more prominent
in girls (ages 7-13) than boys. Treatment includes a low plus lens and/or vision
therapy. This condition is sometimes incorrectly diagnosed by doctors as
hysterical amblyopia.

Stroma- The cornea's middle layer; it consists of lamellae (collagen) and
cells, and makes up most of the cornea.

Sty- A blocked gland at the edge of the lid which has become infected by
bacteria.

Subconjunctival Hemorrhage
- a blood spot on the eye. It occurs when a small blood vessel under the
conjunctiva (the transparent coating that covers the inner eyelid and the white
of the eye) breaks and bleeds. A common condition caused spontaneously from
coughing, heavy lifting, or vomiting. In some cases, it may develop following
eye surgery or trauma. It tends to be more common among those with diabetes,
hypertension, and taking blood thinners (including aspirin). A subconjunctival
hemorrhage is essentially harmless. The blood naturally absorbs within one to
three weeks and no treatment is required. If a mild irritation is present,
artificial tear drops can be used. You can speed up the healing process by
applying cool compresses for the first two days and then warm compresses in the
following days.

Subjective Refraction
- the procedure in which the patient is asked to report on which lens
combination provides the clearest vision. While this is the method of choice for
determining prescription in those able to understand the task and respond to the
examiner, it is less reliable in children.

Suppression of Binocular Vision- when the brain ignores the
image that is seen by one eye. It is the result of weak eye teaming skills
(binocularity).

Suppression Test-
determines if there is any tendency for the visual processing center of the
brain to ignore or suppress visual data from one eye.

Suspensory Ligament- Also called zonule of Zinn. Membrane of fibers
(zonules) that holds the eye's lens in place.

Tactile-
pertaining to the sense of touch.

Titanium- A type of metal alloy that is very strong. Eyeglasses made of
titanium are lightweight, durable and often hypoallergenic.

Tonic- slow,
smooth tension. (See "Fusional Vergence")

Tonic Vergence-
convergence due to the basic tonicity (tension) of the extraocular muscles,
which are responsible, in part, for the distance phoria.Deficient tonic
vergence would result in exophoria and excessive tonic vergence results in
esophoria. (See "Vergence")

Tonometry- an
instrument that measuresthe pressure within the eye, which is known as
intraocular pressure (IOP).

Toric- A lens design with two different optical powers at right angles to
each other for the correction of astigmatism.

Trifocal- A lens design that has three focal areas: a lens for close work
or reading, a lens for mid-distance viewing or arm's length, and a lens for
faraway viewing or driving.
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Tunnel Vision- a
constriction of the visual field that is commonly caused by chronic glaucoma,
retinal degeneration, a tumor, or a brain disorder that interferes with the
fibers that connect the optic nerve to the brain. (Please note that a visual
stress, emotional stress, or emotional trauma can also cause a constriction of
the visual field.) (See "Streff Syndrome".)

Ultraviolet- (UV) The invisible part of the light spectrum
whose rays have wavelengths shorter than the violet end of the visible spectrum
and longer than X rays. UVA and UVB light are harmful to your eyes and skin.
Uvea- Middle layer of the eye, below the limbus, and consisting of the iris,
ciliary body and choroid.

Uveitis- Inflammation of the uvea.

Vectogram-
a
three-dimensional
picture that is used to strengthen the binocularity system. Available in fixed
and variable styles to provide base-in and/or base-out training. 3D glasses are
used to view the picture.

Vergence Facility- a measure of the ease and
speed of the eyes to change from a converging to diverging position.

Vertigo- a
disordered state in which the individual is dizzy or feels that the surrounding
environment is whirling.
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Visagraph
Eye-Movement Recording System - records and measures eye movements while an
individual reads. The system also measures reading efficiency. Specially created
goggles and a computer program are used.
Vision- the
ability to take in information through our eyes and process the information so
that it has meaning.

Vision Therapy (VT) - see "Optometric Vision
Therapy"

Vision Therapy Technician- one who works under the
supervision of an optometrist in evaluating clients and in planning and
implementing vision therapy programs. (See 'COVTT')

Vision Therapist-
Optometrist or an optometric vision therapy technician who develops and
administers vision therapy programs. (Typically this term is referring to a
vision therapy technician rather than an optometrist.)

Please note that there are some individuals that call themselves vision
therapists, but they are not optometrists or vision therapy technicians.

Visual Closure-
the ability to identify or recognize a symbol or object when the entire object
is not visible.

Visual Discrimination-
the ability to discriminate between visible likeness and differences in size,
shape, pattern, form, position, and color. Such as the ability to distinguish
between similar words like "ran" and "run".

Visual Field- the
total area that can be seen while looking straight ahead. (See "Tunnel Vision".)
(Note: Perimetry is the method of testing an eye's field of vision. For more
information, please see "Perimetry".)

Visual Form Dysfunction-
difficulty with figure-ground, form constancy, visual closure, and visual
discrimination. Symptoms include confusion with similar objects, words, or
colors. Vision therapy is a treatment option.

Visual Memory- the
ability to recall and use visual information from the past. (See "Visual
Sequential Memory")

Visual Memory Dysfunction-
difficulty with retention, recall, or recognition of things seen. Symptoms can
include poor spelling and poor recall of visual information. Vision therapy is a
treatment option.

Visual-Motor Dysfunction-
the inability to process and reproduce visual images by writing or drawing.
Symptoms can include poor pencil grip/writing, poor organization on written
page, poor copying/spacing, and excessive erasing. Vision therapy is a treatment
option.

Visual-Motor Integration (VMI)- after visual data is gathered, it is processed and combined in the brain
with information from movement (eye hand coordination).

Visual Pathway-
route of the nerve impulses from the retina along the
optic nerve, and optic nerve radiations to the brain's sensory cortex that is
located at the base of the skull.

Visual Perceptual Disorders-
information processing dysfunctions of the visual system. These dysfunctions can
be a directionality/laterality disorder, visual form dysfunction, visual memory
dysfunction, and visual-motor dysfunction. Vision therapy is a treatment option.
(Also see 'Perceptual Skills')

Visual Perceptual Skills-
the ability to organize and interpret information that is seen and give it
meaning. These information-processing skills include figure-ground, form
constancy, spatial relations, visual closure, visual discrimination, visual
memory, and visualization.

Visual-Sensory Integration-
after visual data is gathered, it is processed and combined in the brain with
information from hearing (auditory-visual integration), balance
(gross-motor/bilateral integration), posture, and movement (visual-motor
integration).

Visual Sequential Memory-
ability to recall a sequence of numbers, letters or objects in the order they
were originally given.

Visual Skills- are
accommodation (eye
focusing), binocularity (eye teaming), and oculomotor skills (eye movement),
which are neuro-muscular abilities that are controlled by
muscles inside and outside of the eye and are networked with the brain.

Visualization-
the ability to crate and manipulate mental pictures of an object or concept on
the basis of past visual experience and memory. Essential in reading and playing
sports.

Vitreous Body- A part of the eye between the lens and the retina,
containing a clear jelly called the vitreous humor.

Wandering Eye(s)-
see "Exotropia".

Wheatstone Stereoscope
-an instrument designed to present separate images to each eye. Each eye can see
independently. Two plane mirrors are joined at one edge at a 90-degree angle and
two target holders, one opposite one mirror and the other, mounted on a screw
base which, when turned, synchronously moves the targets toward or away from
each other. The
Amblyoscope, Troposcope, Synoptophore, and the Bernell Mirror Stereoscope are
examples of this design.

Wraparound-
(wrap) Type of eyeglass frame that curves around the head, from the front to the
side. Wraparound sunglasses tend to offer extra sun protection because the
lenses usually wrap as well.

Yoked Prisms-
a wedge-shaped lens
which is thicker on one edge than the other. The prism bases
(thicker end) are in the same direction for both eyes (up, down, left, or
right). Yoked prisms are used to train or compensate for a binocular dysfunction
(eye teaming problem) or a visual field loss. Sometimes used in optometric
vision therapy programs.